Projection video display apparatus

ABSTRACT

A projection video display apparatus includes: a video projection screen, having a front and a rear surface, arranged in an indoor space. The video projection screen transmits video light from behind the rear surface or in front of the front surface to display video on the front surface. The front surface functions as a video display surface. A video projecting apparatus, arranged in a side of the rear surface or the front surface, enlarges and projects the video light from the rear or front surface. The video projecting apparatus is configured by an optical scanning video projecting apparatus that forms the video by scanning video light composed of coherent light on the video projection screen. The video projection screen guides the video light from the video projecting apparatus toward a direction to the front surface, and causes part of the light in the indoor space to be transmitted therethrough.

TECHNICAL FIELD

The present invention relates to a projection video display apparatusthat projects video onto a transmission projected surface from behind arear surface or in front of a front surface thereof to display thevideo.

BACKGROUND ART

Development of a large and flat video display apparatus is remarkable.In recent years, a video display apparatus using a so-called flat panelsuch as an organic EP panel, for example, is widely diffused in place ofa projection video display apparatus that has been widely diffusedconventionally. However, the projection video display apparatus can bemanufactured at relatively low cost, is light and has excellentportability. In addition to usage as a television receiver, by makinguse of its characteristics, the projection video display apparatus iswidely used as a video display apparatus in education scenes, aconference room or the like, for example.

In a conventional projection video display apparatus, as disclosed inPatent document 1 below, which has been proposed by inventors of thepresent application and has already been disclosed, for example, aprojection video display apparatus that does not require a housing, canbe manufactured at low cost, and has excellent portability is realized.

RELATED ART DOCUMENTS Patent Documents

Patent document 1: Japanese Patent Application Publication No.2011-253130

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the video display apparatus including a rear projection typehas been widely used in order to display broadcast video or an image ofa personal computer. Thus, various improvements suitable for its usageenvironment are required. For that reason, various improvements for theprojection video display apparatus are also required, such as reductionof its manufacture price and power consumption, miniaturization andweight saving, its portability, or its design property in the roominterior in which the apparatus is arranged.

Thus, the present invention provides a projection video displayapparatus that has an extremely new configuration to project video frombehind a rear surface or in front of a front surface thereof in place ofa general configuration of a conventional video display apparatus. Inparticular, it is an object of the present invention to provide animproved projection video display apparatus including reduction of amanufacturing price, reduction of power consumption (ultra-low powerconsumption), miniaturization and weight saving of the apparatus, andits design property.

Means for Solving the Problem

In order to achieve the object described above, according to the presentinvention, as one example, a projection video display apparatus isprovided that includes: a video projection screen arranged in an indoorspace in a state where both surfaces of the video projection screen areexposed to the indoor space, both surfaces including a rear surface anda front surface, the video projection screen being configured totransmit video light to display video on the front surface, the videolight being projected from behind the rear surface or in front of thefront surface of the video projection screen, the front surfacefunctioning as a video display surface; and a video projecting apparatusarranged at a predetermined position in a side of the rear surface orthe front surface of the video projection screen, the video projectingapparatus being configured to enlarge and project the video light fromthe rear surface or the front surface of the video projection screen,wherein the video projecting apparatus is configured by an opticalscanning video projecting apparatus that forms the video by scanningvideo light on the video projection screen, the video light beingcomposed of coherent light, and wherein the video projection screen isconfigured to guide the video light composed of the coherent light fromthe video projecting apparatus toward a direction to the front surfaceof the video projection screen, and to cause part of the light in theindoor space to be transmitted therethrough.

Effects of the Invention

According to the present invention, excellent effects are exhibited thatan improved projection video display apparatus is provided by which:excellent video can be obtained without requiring a housing that coversthe whole apparatus; folding can be carried out easily; portability isexcellent; the apparatus can be manufactured at low cost; powerconsumption can be greatly reduced; and miniaturization and weightsaving of the apparatus, and its design property are included.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a front view illustrating the overall structure of a rearsystem projection board apparatus (rear projection video displayapparatus) according to one embodiment of the present invention;

FIG. 2 is a side view illustrating the overall structure of the rearsystem projection board apparatus (rear projection video displayapparatus) according to one embodiment of the present invention;

FIG. 3 is a top view illustrating the overall structure of the rearsystem projection board apparatus (rear projection video displayapparatus) according to one embodiment of the present invention;

FIG. 4 is a front view illustrating the overall structure of a smallfront system projection board apparatus (front projection video displayapparatus) according to another embodiment of the present invention;

FIG. 5 is a side view illustrating the overall structure of the smallfront system projection board apparatus (front projection video displayapparatus) according to another embodiment of the present invention;

FIG. 6 is a top view illustrating the overall structure of the smallfront system projection board apparatus (front projection video displayapparatus) according to another embodiment of the present invention;

FIG. 7 is a view illustrating an optical scanning video projectingapparatus in the above rear system or front system projection boardapparatus in principle;

FIG. 8 is a view illustrating one example of a structure of an opticalscanning unit that constitutes the above optical scanning videoprojecting apparatus;

FIG. 9 is a view illustrating one example of an operation of the opticalscanning unit that constitutes the above optical scanning videoprojecting apparatus;

FIG. 10 is a view illustrating a change in an oscillation angle due to aphase of the above optical scanning unit;

FIG. 11 is a view illustrating a relationship between the phase and theoscillation angle during a general resonance operation of the aboveoptical scanning unit;

FIG. 12 is a view illustrating a relationship between the phase and ascan coordinate (or an incident coordinate) during the general resonanceoperation of the above optical scanning unit;

FIG. 13 is a view illustrating a concrete configuration (circularFresnel lens) of a semitransparent screen in the above rear systemprojection board apparatus;

FIG. 14 is a view illustrating a concrete configuration (linear Fresnellens) of the semitransparent screen in the above rear system projectionboard apparatus;

FIG. 15 is a partially enlarged sectional view illustrating a moredetailed configuration of the above semitransparent screen;

FIG. 16 is a view illustrating a concrete configuration (circularFresnel lens) of the semitransparent screen in the above front systemprojection board apparatus;

FIG. 17 is a view illustrating a concrete configuration (linear Fresnellens) of the semitransparent screen in the above front system projectionboard apparatus;

FIG. 18 is a partially enlarged sectional view illustrating a moredetailed configuration of the above semitransparent screen;

FIG. 19 is a view illustrating a reflection characteristic graph of anS-polarized light wave that is used in the above optical scanning videoprojecting apparatus;

FIG. 20 is a view illustrating another concrete configuration of thesemitransparent screen in the above rear or front system projectionboard apparatus;

FIG. 21 is a view illustrating the optical scanning video projectingapparatus in the above rear system and front system projection boardapparatus according to an embodiment;

FIG. 22 is a front view illustrating a basic optical configuration ofthe above optical scanning video projecting apparatus according to afirst embodiment (in which an optical scanning apparatus is arrangedunder an image plane);

FIG. 23 is a side view illustrating the basic optical configuration ofthe above optical scanning video projecting apparatus according to thefirst embodiment (in which the optical scanning apparatus is arrangedunder the image plane);

FIG. 24 is an enlarged view of a projection unit in the above opticalscanning video projecting apparatus according to the first embodiment;

FIG. 25 is an enlarged view of a freeform surface lens in the aboveoptical scanning video projecting apparatus according to the firstembodiment;

FIG. 26 is a configuration view for confirming optical path interferenceof the above optical scanning video projecting apparatus according tothe first embodiment;

FIG. 27 is a distortion performance diagram of the above opticalscanning video projecting apparatus according to the first embodiment;

FIG. 28 is a relationship view between a phase and an incident angle ofthe above optical scanning video projecting apparatus according to thefirst embodiment;

FIG. 29 is a relationship view between the phase and an incidentcoordinate of the above optical scanning video projecting apparatusaccording to the first embodiment;

FIG. 30 is a coordinate view illustrating respective optical surfaces ofa main ray in the above optical scanning video projecting apparatusaccording to the first embodiment in which a two-dimensional scanningarea is divided into 5×5;

FIG. 31 is a ray diagram illustrating a shape of the freeform surfacelens in a main scanning direction of the above optical scanning videoprojecting apparatus according to the first embodiment;

FIG. 32 is a shape diagram of the freeform surface lens and mirror in avertical scanning direction of the above optical scanning videoprojecting apparatus according to the first embodiment;

FIG. 33 is a view illustrating a basic optical configuration diagram ofthe above optical scanning video projecting apparatus according to asecond embodiment;

FIG. 34 is an enlarged view of an optical scanning video projectingapparatus in the above optical scanning video projecting apparatusaccording to the second embodiment;

FIG. 35 is an enlarged view of a freeform surface lens in the aboveoptical scanning video projecting apparatus according to the secondembodiment;

FIG. 36 is a distortion performance diagram of the above opticalscanning video projecting apparatus according to the second embodiment;

FIG. 37 is a basic optical configuration diagram of the above opticalscanning video projecting apparatus according to a third embodiment;

FIG. 38 is an enlarged view of an optical scanning video projectingapparatus in the above optical scanning video projecting apparatusaccording to the third embodiment;

FIG. 39 is an enlarged view of a freeform surface lens in the aboveoptical scanning video projecting apparatus according to the thirdembodiment;

FIG. 40 is a distortion performance diagram of the above opticalscanning video projecting apparatus according to the third embodiment;

FIG. 41 is a top view illustrating a first usage form of the othermodification example of the optical scanning apparatus in the aboveoptical scanning video projecting apparatus;

FIG. 42 is a side view illustrating the first usage form of the othermodification example of the optical scanning apparatus in the aboveoptical scanning video projecting apparatus;

FIG. 43 is a view illustrating a second usage form of the othermodification example of the optical scanning apparatus in the aboveoptical scanning video projecting apparatus;

FIG. 44 is a view illustrating a third usage form of the othermodification example of the optical scanning apparatus in the aboveoptical scanning video projecting apparatus;

FIG. 45 is a view illustrating a basic configuration of a scanningprojection apparatus regarding uniformity in brightness of a scanscreen;

FIG. 46 is an explanatory drawing for explaining a scanning state oflaser beam that scans an image plane of the above optical scanningapparatus;

FIG. 47 is a schematic view illustrating a light emitting point of asemiconductor laser in the above optical scanning apparatus;

FIG. 48 is a basic configuration diagram for explaining first technicalmeans of the above optical scanning apparatus;

FIG. 49 is an explanatory drawing for explaining a scanning state oflaser beam that scans an image plane by means of the first technicalmeans of the above optical scanning apparatus;

FIG. 50 is an explanatory drawing for explaining a scanning state oflaser beam that scans an image plane by means of second technical meansof the above optical scanning apparatus;

FIG. 51 is an explanatory drawing for explaining a scanning state oflaser beam that scans an image plane by means of the other technicalmeans of the above optical scanning apparatus; and

FIG. 52 is a view illustrating a modification example in which anelectrostatic type pressure sensor for the above projection boardapparatus is incorporated into a screen.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, one embodiment of the present invention will be describedin detail with reference to the accompanying drawings. In the followingdrawings, the same reference numeral is assigned to components eachhaving a common function, and explanation of components that have beenexplained once will be omitted thereafter.

FIG. 1 to FIG. 3 accompanied thereto first respectively illustrate afront view, a side view, and a top view of the overall structure of aso-called rear system projection board apparatus (that is, rearprojection video display apparatus) according to one embodiment of thepresent invention. In these drawings, a reference numeral 130 denotes asemitransparent projection screen whose detailed structure will bedescribed below. A landscape-oriented screen in which aspect ratio of aprojection (display) surface thereof is 16:9 is illustrated, forexample. This semitransparent screen 130 is surrounded by a supportframe 111. A handle 112 is installed substantially at the center of asupport frame stiffened member 110 provided on a lower portion of thesemitransparent screen 130. The handle 112 protrudes to a side of adisplay surface in a “C-shaped” or “U-shaped” manner.

Thus, the semitransparent screen 130 described above is verticallyarranged in an upright state, that is, on a floor surface by a screenholder (stand) 113 in an indoor space such as a classroom or aconference room, for example. More specifically, a screen holder 114whose external shape is a box-like shape is installed on an upperportion of the screen holder (stand) 113. The screen 130 described aboveis detachably mounted and fixed on a top surface of the screen holder114. Further, a leg 115 whose external form is a substantially ellipticshape is formed on a lower end of this screen holder (stand) 113 (seeFIG. 3). Apart of the leg 115 is cut out. Moreover, casters 116 formovement are provided on a bottom surface of the leg 115. This realizesa projection board that can move easily as the whole apparatus.

Moreover, a member for arranging an optical scanning video projectingapparatus therein, that is, a projector installation part 117 isdetachably provided at a side of a rear surface of the screen holder 114described above. A detailed structure of the projector installation part117 will be described later. Note that a reference numeral 118 denotes awall portion that is a part of the projector installation part 117 andforms a storage space for the optical scanning video projectingapparatus. According to the configuration described above, as isapparent from the drawings, it is possible to arrange the opticalscanning video projecting apparatus at a desired position with respectto the semitransparent screen 130 described above by mounting theoptical scanning video projecting apparatus on the projectorinstallation part 117. Further, a reference numeral 119 in the drawingsdenotes a transmissive window, which is installed above a part of theprojector installation part 117 described above, for causing video lightfrom the optical scanning video projecting apparatus to transmit towardthe outside (that is, toward the semitransparent screen 130). Forexample, the transmissive window may be provided merely as a space.Alternatively, the transmissive window may be formed by fitting atransparent body such as glass therein.

FIG. 4 to FIG. 6 are respectively a front view, a side view, and a topview illustrating the overall structure of a so-called front systemprojection board apparatus (that is, front projection video displayapparatus) according to another embodiment of the present invention, forexample. The front system projection board apparatus is small one fortable use that can be mounted on a top surface of a table or the like.In these drawings, a reference numeral 130 also denotes asemitransparent projection screen. This semitransparent screen 130 issurrounded by the support frame 111. A screen holder 114 with asubstantially elliptic shape is provided at a substantially centralportion of the support frame stiffened member under the semitransparentscreen 130. The screen 130 described above is detachably fixed on thescreen holder 114.

A portion for arranging the optical scanning video projecting apparatustherein, that is, a projector installation part 117 is formed at a sideof a front surface of this screen holder 114. Note that FIG. 5illustrates a state where an optical path folding mirror (freeformsurface mirror) 3 protrudes from the projector installation part 117.

Subsequently, FIG. 7 illustrates an optical scanning video projectingapparatus 10 in principle. The optical scanning video projectingapparatus 10 constitutes an optical scanning video projecting apparatusthat projects desired video onto the semitransparent screen 130described above in the rear system or front system projection boardapparatus (rear surface or front projection video display apparatus)according to the present invention. Namely, in FIG. 7, laser beam from alight source 4 is reflected by a scanning mirror (optical scanning unit)1 having a swing shaft, whereby it is possible to scan the laser beam.Conceptually, each pixel 201 that has been modulated istwo-dimensionally scanned on an image plane along a scan locus 202.

Next, details of a two-dimensional deflection operation in the opticalscanning unit 1 described above will be described with reference to FIG.8. In the optical scanning unit 1 illustrated in FIG. 8, a scanningmirror surface 1 a is coupled to first torsional springs 1 b. Thescanning mirror surface 1 a deflects laser beam with a reflection angle.The first torsional springs 1 b are arranged coaxially with the scanningmirror surface 1 a so as to put the scanning mirror surface 1 atherebetween and be opposed to each other. The torsional springs 1 b arecoupled to a holding member 1 c. Moreover, the holding member 1 c iscoupled to second torsional springs 1 d. Permanent magnets and coils(not illustrated in FIG. 8) are arranged at positions substantiallysymmetrical about each of the torsional springs 1 b and 1 d. These coilsare formed in substantially parallel to the mirror surface 1 a of thescanning mirror 1. When the mirror surface 1 a of the scanning mirror 1is in a stationary state, a magnetic field substantially parallel to themirror surface 1 a is generated. When current flows into the coils, aLorentz force substantially Perpendicular to the mirror surface 1 a isgenerated on the basis of a Fleming's left hand rule.

This causes the mirror surface 1 a to swing to a position at which theLorentz force balances restoring forces of the torsional springs 1 b and1 d. With respect to the torsional spring 1 b, by supplying alternatingcurrent with resonance frequency of the mirror surface 1 a to each ofthe coils, the mirror surface 1 a carries out a resonance operation.Similarly, with respect to the torsional spring 1 d, by supplyingalternating current with resonance frequency of a combination of themirror surface 1 a and the holding member 1 c to each of the coils, themirror surface 1 a, the torsional spring 1 b, and the holding member 1 ccarry out a resonance operation. This makes it possible to carry out theresonance operations for two directions based on the different resonancefrequencies.

More specifically, in FIG. 9, in a case where a swinging angle of thescanning mirror 1, which is a reflective surface of the optical scanningunit, is set to β/2, a scanning angle that is an angle of a reflectedray is changed into β, which is twice the swinging angle. Here, in acase where no optical element is arranged between the scanning mirror 1and an image plane 20, the scanning angle β is equal to an incidentangle α with respect to the image plane 20. Therefore, a size of a scanimage with respect to a certain projection distance is determined by theswinging angle β/2 of the scanning mirror 1.

Next, a general resonance action that is an operation of the scanningmirror 1 will be described with reference to FIG. 10. In a case wherethe scanning mirror 1 with the swinging angle ±β/2 is driven by aresonance operation, that is, in a sinusoidal shape, a direction of thescanning mirror 1 changes in a range of ±β/2 in the sinusoidal shape.Specifically, FIG. 11 illustrates an example of a case where thescanning mirror 1 with a swinging angle of ±5.3° is used. Here, thescanning angle becomes ±10.6° that is twice, and the incident angle withrespect to the image plane 20 also becomes ±10.6°. Thus, a scancoordinate illustrated in FIG. 12 is a scan coordinate on the imageplane 20 in a case where a space for arrangement of any optical elementis secured, and has a sinusoidal characteristic similar to that in FIG.11.

Note that as a driving system of the scanning mirror 1, in addition to aresonance type mirror that sinusoidally changes a swinging angle, thereis a galvanometer mirror that changes a swinging angle in a sawtoothwave-like manner. However, the resonance type mirror whose drivefrequency is high is suitable for display with high resolution.

Further, in the above explanation, the optical scanning video projectingapparatus 10 configured to project video onto the semitransparent screen130 described above was arranged under the semitransparent screen 130.More specifically, the optical scanning video projecting apparatus 10was arranged adjacent to a part of a periphery at a rear surface sidethereof, that is, is arranged within the projector installation part 117provided substantially at a central portion along a lower edge of thescreen. However, arrangement of the optical scanning video projectingapparatus 10 is not limited to the above example. It is obvious for aperson having ordinary skill in the art that the optical scanning videoprojecting apparatus 10 may be installed along an upper edge or a sideedge of the screen 130 in place of the above, for example. Further,although it will be described later, the number of the optical scanningvideo projecting apparatus 10 provided so as to be adjacent to a part ofthe periphery of the screen 130 is not limited to one as describedabove. A plurality of optical scanning video projecting apparatuses 10may be installed.

Subsequently, FIG. 13 and FIG. 14 illustrate a concrete configuration ofthe semitransparent screen 130 in the rear system projection boardapparatus (rear projection video display apparatus) described above.This semitransparent screen 130 is configured by a board made ofpolycarbonate or the like, a sheet-like resin material sheet such as aPET sheet, or a glass plate, for example. As is also apparent from thedrawings, a large number of optical path changers 61 are formed on arear surface of the semitransparent screen 130 (that is, a light sourceside opposite to an observer side). The optical path changers 61 have across section of a continuous triangular shape (sawtooth wave shape),and have an action to refract the light (laser beam) described above bywhich a scan screen is formed and change it into light toward the sideof the observer (that is, a viewer). Namely, the optical path changers61 change a direction of the light into a direction substantiallyperpendicular to the scan screen to emit the light to a scanning imageviewing side. As a concrete example of these optical path changers 61,for example, the optical path changers 61 may be formed as an(eccentric) circular Fresnel lens as illustrated in FIG. 13, or may beformed as a linear Fresnel lens as illustrated in FIG. 14.

Moreover, as illustrated in FIG. 15(a), the semitransparent screen 130may also be formed so that flat portions 62 each having a predetermineddistance are respectively provided between adjacent optical pathchangers 61 (semitransparent type). Note that in the present embodiment,these optical path changers 61 are formed at pitches (or intervals) fromabout 30 μm to 100 μm as one example. In addition, as illustrated inFIG. 15(b), a plate-like transparent protective plate 65 may also beprovided on the rear surface of the semitransparent screen 130 (that is,a surface on which the optical path changers 61 are formed).

Further, FIGS. 16 and 17 illustrate a concrete configuration of thesemitransparent screen 130 in the front system projection boardapparatus (front projection video display apparatus) described above.This semitransparent screen 130 has a cross section of a continuoustriangular shape (sawtooth wave shape) on its rear surface (that is, aside opposite to the observer side). A large number of optical pathchangers 61 are formed thereon. Each of the optical path changers 61 hasa function to refract light (laser beam) that enters from a frontsurface (viewing side) of the semitransparent screen 130 to form thescan screen described above and to change the light into light travelingtoward the observer (that is, the viewer) side. Namely, these opticalpath changers 61 change a direction of the light into a directionsubstantially perpendicular to the scan screen to emit the light to thescanning image viewing side. As a concrete example of these optical pathchangers 61, for example, the optical path changers 61 maybe formed asan (eccentric) circular Fresnel lens as illustrated in FIG. 16, or maybe formed as a linear Fresnel lens as illustrated in FIG. 17.

Moreover, as illustrated in FIGS. 15(a) and 15(b), the semitransparentscreen 130 may also be formed so that flat portions 62 each having apredetermined distance are respectively provided between adjacentoptical path changers 61 (semitransparent type). Note that a refractionfactor of material or a Fresnel angle of these optical path changers 61may be optimized so that a video ray is totally reflected.Alternatively, as illustrated in FIG. 15(b), a reflective film 64 formedfrom a metal film or a metallic multilayer whose reflection factorbecomes higher with respect to a specific polarized wave may be providedon an inclined surface 63. In the present embodiment, these optical pathchangers 61 are formed at pitches (or intervals) from about 30 μm to 100μm as one example. In addition, a plate-like transparent protectiveplate 65 is provided on the rear surface of the semitransparent screen130 (that is, a surface on which the optical path changers 61 areformed).

Note that as described above, a metal film made of aluminum or the likeor a metallic multilayer made of Ti, Nb, or Si is formed on each of theinclined surfaces 63 that form these optical path changers 61, forexample, thereby forming a reflective surface for the light (laserbeam). In a case where an oblique projection optical system is used likethe present embodiment, an eccentric Fresnel lens whose Fresnel centeris out of the scan screen is particularly suitable. On the other hand,according to the linear Fresnel lens, for example, manufacture thereofis relatively easy by a roll process, and it is suitable for massproduction. Therefore, it is possible to manufacture a large screen atlow cost.

Further, according to the plate-like transparent protective plate 65provided on the surface of the semitransparent screen 130 on which theoptical path changers 61 are formed, it is possible to protect thesemitransparent screen 130 against mechanical impact from the rearsurface thereof. In addition, by shielding the optical path changers 61from outside air, dust or the like in the air is hardly deposited, andthis makes it possible to maintain the semitransparent screen 130 ingood condition for a long time.

According to such a screen 130, in a case where a total reflectionsystem is adopted in order to reduce a reflection loss on an incidentsurface, it is possible to realize an apparatus that can acquire anexcellent scanning image whose reflection loss is small, in other words,to realize an apparatus of ultra-low power consumption with high usageefficiency of light.

Further, on the other hand, according to the screen 130 composed of thesemitransparent type sheet illustrated in FIG. 13 to FIG. 18 describedabove, in a case where video is not projected, the screen 130 becomessemitransparent when viewed from the observer side. Therefore, it ispossible to obtain advantage that various improvements for designproperty of the whole rear projection video display apparatus arepossible in addition to a sense of existence and the like in the roominterior in which the apparatus is arranged. In particular, it isthought advantage that in a case of presentation to a client or astudent who faces a user of the apparatus via an intervening table orthe like, for example, the small front system projection board apparatusfor table use as illustrated in FIG. 4 to FIG. 6 can confirm a state ofthe partner via the semitransparent screen 130.

In the screen 130 described above, by appropriately setting a thicknessof a metal film made of aluminum or the like, which is to be formed onthe inclined surface 63 of each of the optical path changers 61, itbecomes possible to obtain desired transparent (or a degree ofsemitransparent). As one example, for example, by setting a thickness ofthe metal film made of aluminum to about 70 nm to 80 nm, asemitransparent screen 130 in which a transmission factor thereof is 50%and a reflection factor thereof is 50% with respect to light isobtained.

In addition, it is preferable that as illustrated in FIG. 19, the laserbeam emitted from the optical scanning video projecting apparatus andreflected to a predetermined direction by the optical path changers 61of the screen 130 described above is an S-polarized light wave inconsideration of its reflection characteristic. For that reason, afilter of the like for converting a P-polarized light wave into anS-polarized light wave may be provided at an output unit of the opticalscanning video projecting apparatus that will be described below indetail.

As is apparent from the above, according to the rear system or frontsystem projection board apparatus (rear/front projection video displayapparatus) of the present invention described above, by adopting thesemitransparent screen 130 described above together with the opticalscanning video projecting apparatus 10 that uses coherent light from thelight source in the scanning mirror 1 (optical scanning unit), that is,reflects and scan the laser beam to form video, excellent video can beobtained without requiring a housing that covers the whole apparatusunlike a conventional apparatus. This makes it possible to carry outfolding easily. For that reason, it is possible to provide the improvedrear projection video display apparatus with excellent portability thatcan be manufactured at low cost, and in which excellent reduction ofpower consumption, miniaturization and weight saving of the apparatus,and its design property are included.

In the above explanation, the general optical scanning video projectingapparatus 10 in the rear projection video display apparatus has beenexplained as one that scans the laser beam, which is the coherent lightfrom the light source, by the scanning mirror (optical scanning unit) toform video. However, the present invention is not limited to it, and afurther improved optical scanning video projecting apparatus can beadopted.

<Details of Optical Scanning Video Projecting Apparatus>

Thus, a configuration, behavior and an operation of the optical scanningvideo projecting apparatus 10 constituting the rear system projectionboard apparatus (rear projection video display apparatus) describedabove according to another embodiment, which include its modificationexample will be described below in detail.

As illustrated in FIG. 20, this optical scanning video projectingapparatus 10 basically includes: the light source 4 that emits a laserbeam; and an optical scanning unit that carries out optical scanning intwo directions including a main scanning direction (horizontaldirection) and a vertical scanning direction (vertical direction) byusing the scanning mirror 1 that is a resonance type mirror. The opticalscanning video projecting apparatus 10 has a function to scan anddeflect the laser beam emitted by the light source 4 in the mainscanning direction and the vertical scanning direction.

In order to execute two-dimensional scanning corresponding to eachscanning line of television, by first carrying out scanning pixels inthe horizontal direction while carrying out the optical scanning of oneround trip in the vertical direction, it is possible to carry outscanning for one scanning line. For example, in order to carry outdisplay with horizontal 800 pixels and vertical 600 pixels by verticalfrequency of 60 Hz, 300 round trips are required because there are 600pixels in the horizontal direction. Thus, it is necessary that thescanning mirror 1 can be driven with high frequency of 60×300=18000 Hz(18 kHz). It is increasingly necessary to drive the scanning mirror 1with high frequency as resolution (the number of pixels) to be displayedbecomes larger. Table 1 below indicates a relationship between displayedpixels and horizontal scanning frequency (horizontal scanning number).In HD correspondence of horizontal 1920 pixels and vertical 1080 pixels,the frequency becomes 38.9 kHz, whereby further speeding up is required.In addition, in order to realize a large scan image with respect to ashort projection distance, it is necessary that the swinging angle ofthe scanning mirror 1 is made larger.

TABLE 1 RESOLUTION VGA SVGA XGA SXGA HD (640 × 480) (800 × 600) (1024 ×768) (1280 × 1024) (1920 × 1080) HORIZONTAL 18 kHz 22.5 kHz 28.8 kHz38.4 kHz 38.9 kHz SCAN FREQUENCY

Thus, both driving the scanning mirror 1 at further high speed anddriving it with a large swinging angle cause loads of the torsionalsprings 1 b and 1 d, which are mechanism components of moving parts, tobe increased. Therefore, in a conventional resonance type mirror, highfrequency and the swinging angle of the scanning mirror 1 have arelationship of tradeoff.

Therefore, in a conventional optical scanning apparatus (see JapanesePatent Application Publication No. 2010-139687, for example), in orderto display an image with large resolution (the number of pixels), aswinging angle of a mirror becomes smaller as tradeoff. Thus, in orderto display an image with a predetermined size, a large projectiondistance was required. In addition, there has been a problem that amovement locus of a scan coordinate on an image plane becomes asinusoidal shape, and linearity is thus bad.

Further, in sinusoidal shape swing of the scanning mirror, a rapidchange and a slow change in the angle of the scanning mirror appearperiodically. In a case where a laser beam scans the image plane only bythis sinusoidal swing of the scanning mirror and an angle change of thescanning mirror is fast, a change in the scanning position on the imageplane also becomes fast. In a case where the angle change of thescanning mirror is slow in such a condition, the change in the scanningposition on the image plane also becomes slow. Therefore, light anddarkness corresponding to a sinusoidal wave are generated on the imageplane.

In a case where the laser beam is modulated at equal intervals withrespect to time and the angle change of the scanning mirror is fast, forthe same reason, pixels are roughly arranged on the image plane. In acase where the angle change of the scanning mirror in such a condition,the pixels are densely arranged on the image plane. Therefore, atwo-dimensional image in which linearity is greatly deteriorated isgenerated.

Here, by executing circuit processing to thin out the laser beam in asinusoidal light portion in which pixel distribution is dense, it ispossible to improve only light and darkness on the image plane. However,the linearity of the two-dimensional image cannot be improved, and newproblems of an increase in a circuit scale and reduction of lightquantity are generated. Note that by modulating the laser beam whilematching timing of arrangement of the pixels on the image plane, thelinearity can also be improved. However, the circuit scale is increasedmore and more.

As measures of such problems, in a conventional optical scanningapparatus (see Japanese Patent Application Publication No. 2005-234157,for example), a “scanning optical system (scanning mirror and prism)”having a plurality of reflective surfaces in addition to a scanningmirror has been proposed. However, in a case where a shape error of anoptical component in its manufacturing process, or eccentricity orfalling of an optical component in assembly occurs, then a change in aray angle on the mirror surface is about twice compared with a lenssurface that is a transparent surface. Therefore, manufacture of theoptical system using the mirror surface frequently becomes drasticallydifficult.

Moreover, in another conventional technology, a “two-dimensionalscanning optical system (scanning mirror, prism, a scanning lens)”having a plurality of reflective surfaces in addition to a scanningmirror has been proposed (see Japanese Patent Application PublicationNo. 2006-178346, for example). However, in a case where a shape error ofan optical component in its manufacturing process, or eccentricity orfalling of an optical component in assembly also occurs, then similarlyto the above, a variation in a ray angle on the mirror surface is abouttwice compared with a lens surface that is a transparent surface.

In addition, in an optical system using a plurality of mirror surfaces,in order to secure optical paths before and after reflection of a laserbeam on the mirror surface, it is necessary to make an interval beforeand after the mirror surface larger. Thus, there is also a problem thata size of the whole optical system is to be increased.

Therefore, in the optical scanning video projecting apparatus, theproblem of light quantity distribution, the problem of the linearity,and a problem of degradation of reliability due to an increase in amechanical load to the scanning mirror exist.

Further, in the optical scanning video projecting apparatus, a lasersource is generally used as the light source. In that case, thegenerated laser beam is coherent light. Therefore, a random phase isadded thereto when the laser beam is reflected by a general screensurface (rough surface), and the reflected light becomes scatteringrays. Then, rays scattered by different points on the rough surface areoverlapped and interfere by means of space propagation, whereby specklesthat forms a random interference pattern are generated and glare occursin a projected image. Depending on conditions, image quality isdeteriorated extremely.

Further, in an optical scanning apparatus in which a semiconductor laseror the like with a small light emitting point is used as a light source,emission of a laser beam with energy, which exceeds a permitted value,in a solid angle connecting the light source to the pupil of theobserver causes a risk that the retina is burned out. Therefore, itslight quantity is restricted, and necessary brightness may not beobtained.

The optical scanning video projecting apparatus adopted in the rearsystem projection board apparatus (rear projection video displayapparatus) according to the present invention is achieved in view of theproblems described above. The optical scanning video projectingapparatus has excellent light use efficiency as an image displayapparatus using an oblique optical system, and excellent scanperformance with respect to increase in angle and/or linearity. Thismakes it possible to suppress speckles. Therefore, an excellent rearprojection video display apparatus is achieved in which sufficientbrightness can be obtained under bright environment.

Note that in order to solve the problems described above, the adoptedoptical scanning apparatus is configured by: a light source configuredto supply a laser beam as a light beam, for example; an optical scanningunit configured to scan light emitted from the light source by means ofreciprocating movement of a reflective surface; and an optical systemconfigured to enlarge a scanning angle of the scanned light, in such aconfiguration, the optical system is configured to have one curvedsurface lens at a side of the light source and one curved surface mirrorat a side of an image plane. In order to obtain higher opticalperformance, it is preferable that a shape of each of the curved surfacelens and the curved surface mirror described above is a freeform surfacewhose freedom degree of design is large.

With respect to a plane defined by an incident ray and a reflected rayby the curved surface mirror when the optical scanning unit remainsstationary at the center of a scanning area, a long side of thetwo-dimensional scanning area on the image plane is configured by adirection that becomes a more parallel positional relationship comparedwith a short side thereof. A direction of larger one of deflectionangles of the reflective surface in two scanning directions isconfigured by a direction corresponding to a long side direction of thescanning area.

Moreover, the optical scanning unit is arranged by an angle of 45° orsmaller with respect to an optical axis connecting the laser source tothe optical scanning unit. The curved surface lens and the curvedsurface mirror are arranged eccentrically from the optical axis, wherebythe optical scanning unit can be arranged so that scanning lightreflected by the curved surface mirror does not enter the curved surfacelens again even though a distance between the curved surface mirror andthe image plane is set to sufficient short. Therefore, miniaturizationof the apparatus can be realized.

On the other hand, in order to suppress speckles, monochromic lasersources are not respectively used as light sources with red, Green, andblue, and each of a plurality of light sources with adjacent wavelengthsis used together. Moreover, by polarizing and synthesizing one of theplurality of light sources with the adjacent wavelengths as S-polarizedlight and the other as P-polarized light, it is possible to furtherachieve the effect. By setting a surface of the curved surface mirror toa surface on which plural kinds of surface roughness are mixed at thesame time, coherency of a laser is reduced to suppress the speckles.

By providing the surface of the curved surface mirror described above asa rough surface and causing a part thereof to have a scatteringcharacteristic to spuriously widen an area of a light emitting point andbecome a two-dimensional light source, light quantity is increased whilesatisfying safety standard. Further, as described above, by using theplurality of light sources with adjacent wavelengths together withoutusing monochromic laser sources with red, green, and blue, it ispossible to improve brightness, and it is also possible to widen a colorreproduction range.

Hereinafter, a configuration of each unit for realizing the opticalscanning apparatus described above, its function and effect will bedescribed below in detail.

A basic configuration of the whole optical scanning apparatus describedabove, which is illustrated in FIG. 20, is roughly divided into theoptical scanning video projecting apparatus 10, a structure 30 thatholds the optical scanning video projecting apparatus 10, and the imageplane 20. In such a configuration, the laser beam emitted from the lightsource 4 is two-dimensionally deflected by the optical scanning unit 1.This deflected laser beam receives improvement of linearity and anaction of an increase in angle with a freeform surface lens 2 that is arefractive system lens and a freeform surface mirror 3 that is areflective mirror, and is displayed on the image plane 20 as atwo-dimensional scan image in which the image is rectangular(two-dimensional) and light quantity distribution is even.

FIG. 21 illustrates one example of arrangement of the freeform surfacemirror 3. In FIG. 21, the freeform surface mirror 3 is arranged so thatwith respect to a first plane (an X-Z plane by definition of acoordinate system in Table 2) defined by an incident ray and a reflectedray in a freeform surface mirror when the optical scanning unit 1remains stationary at the center of a scanning area, a long side of thetwo-dimensional scanning area on the image plane 20 approaches aparallel positional relationship compared with a short side thereof.This reason is as follows. By arranging the freeform surface mirror 3obliquely with respect to a ray at a long side for which a scanningamount is large, a coordinate area in which rays scanned with a scanningangle that becomes twice a predetermined swinging angle are reflected bythe freeform surface mirror 3 becomes wider. Therefore, a freedom degreeof a shape of the freeform surface mirror 3 is increased.

<First Embodiment>

Subsequently, a basic configuration of an optical system in an opticalscanning apparatus including the freeform surface lens 2 described abovewill be described with reference to FIG. 22 to FIG. 32.

FIG. 22 and FIG. 23 are a basic configuration diagram of the opticalsystem in the optical scanning apparatus according to a firstembodiment. FIGS. 22 and 23 illustrate a state where rays emitted fromthe optical scanning video projecting apparatus 10 reach divided pointsof 5×5 on an image plane 20. A reference numeral 40 in these drawingsdenotes a housing of the optical scanning video projecting apparatus 10.

Further, FIG. 24 illustrates main parts constituting the opticalscanning video projecting apparatus 10. In this drawing, scanning of alaser beam emitted from the light source 4 (see FIG. 20) is deflected byswing of the scanning mirror 1, and the laser beam then passes throughthe freeform surface lens 2 and the freeform surface mirror 3 to reachthe image plane 20 (not illustrated in the drawings).

FIG. 25 is a detail drawing of the freeform surface lens 2 describedabove. The freeform surface lens 2 is configured by a first freeformsurface lens 2 a and a second freeform surface lens 2 b. A physicallength of a portion through which laser beams corresponding to alongitudinal direction of a scan screen in the second freeform surfacelens 2 b pass becomes larger compared with a portion through which laserbeams corresponding to a short direction of the scan screen.

Moreover, in a portion at which the laser beams corresponding to thelongitudinal direction of the scan screen in the freeform surface mirror3 illustrated in FIG. 24 are reflected, a shape of a convex surfacebecomes stronger toward the scan screen compared with a portion at whichthe laser beams corresponding to the short direction of the scan screenare reflected.

Note that in FIG. 24 and FIG. 25, the optical scanning video projectingapparatus 10 is displayed along a direction by which it is easier tounderstand shapes of these optical elements.

Moreover, in the ray diagram of FIG. 22 described above, it is hard tounderstand that the ray reflected by the freeform surface mirror 3 isnot irradiated to the freeform surface lens 2 again, that is, presenceor absence of optical path interference. Therefore, FIG. 26 illustratesa ray diagram in a direction by which it is found that no optical pathinterference occurs.

In addition, Table 2 and Table 3 below indicate one example of opticaldata.

TABLE 2 DISTANCE NAME OF CONTENT OF SURFACE RADIUS OF BETWEEN GRASSECCENTRICITY NAME NUMBER SHAPE CURVATURE SURFACES MATERIAL AND FALLINGLASER LIGHT (0) SPHERE ∞ 5 SOURCE INCIDENT (1) SPHERE ∞ 0 PUPIL MEMS (2)SPHERE ∞ 0 REFLECTIVE DECENTER & SURFACE RETURN DUMMY (3) SPHERE ∞ −8.5NORMAL SURFACE ECCENTRICITY FREEFORM (4) XY ∞ −2.7 PMMA 25 DECENTER &SURFACE POLYNOMIAL RETURN LENS SURFACE (5) XY ∞ −0.961 DECENTER &POLYNOMIAL RETURN SURFACE FREEFORM (6) XY ∞ −3.5 PMMA 25 DECENTER &SURFACE POLYNOMIAL RETURN LENS SURFACE (7) XY ∞ −60 DECENTER &POLYNOMIAL RETURN SURFACE FREEFORM (8) XY ∞ 0 REFLECTIVE DECENTER &SURFACE POLYNOMIAL SURFACE RETURN MIRROR SURFACE DUMMY (9) SPHERE ∞ 100NORMAL SURFACE ECCENTRICITY IMAGE PLANE (10) SPHERE ∞ 0 NORMALECCENTRICITY AMOUNT OF AMOUNT OF ECCENTRICITY (mm) FALLING (°) X YAROUND AROUND SURFACE ECCENTRICITY ECCENTRICITY X AXIS Y AXIS NAMENUMBER xde yde ade bde LASER LIGHT (0) SOURCE INCIDENT (1) PUPIL MEMS(2) 0 0 0 −40.860 DUMMY (3) 0 0 0 −90.000 SURFACE FREEFORM (4) −0.090 00 22.106 SURFACE (5) 0.340 0 0 5.090 LENS FREEFORM (6) 1.987 0 0 21.588SURFACE (7) 2.307 0 0 −4.349 LENS FREEFORM (8) 63.719 0 0 80.166 SURFACEMIRROR DUMMY (9) 0 0 0 128.061 SURFACE IMAGE PLANE (10) 270 0 0 0

TABLE 3 FREEFORM FREEFORM FREEFORM SURFACE SURFACE LENS SURFACE LENSMIRROR FOURTH FIFTH SIXTH SEVENTH EIGHTH CODE SURFACE SURFACE SURFACESURFACE SURFACE c 1/R 0 0 0 0 0 K K 0 0 0 0 0 C2 X 0.3496245630.269927984 −0.185371844 −0.309182354 −0.628649481 C4 X² 0.04128861−0.012182237 −0.054746638 0.003698041 −0.009288099 C6 Y² −0.141017861−0.048519056 0.764937711 0.021587641 0.002196752 C7 X³ −0.021500470.004069698 0.005633624 −0.005692978 0.000701226 C9 XY² −0.0172567070.025427159 0.108572457 −0.00623869 0.000244257 C11 X⁴ −0.0008216756.1483E−04 0.00550315 1.8254E−04 2.0585E−05 C13 X²Y² 0.0148138838.7481E−03 0.021244535 2.9920E−03 −1.1730E−05 C15 Y⁴ −0.026216902−3.1692E−01 −0.395137143 2.3554E−03 −9.4200E−07 C16 X⁵ 0.0001104431.1006E−04 −0.000208594 1.3819E−04 −7.8182E−07 C18 X³Y² −0.0026626447.4408E−03 −0.001397694 −3.8605E−04 −6.2747E−07 C20 XY⁴ 0.0465317646.1055E−02 −0.100446252 −6.6014E−04 8.1691E−08 C22 X⁶   4.37627E−052.3341E−05 0.000292687 4.9997E−06 2.0093E−08 C24 X⁴Y² 0.003196906−4.1073E−04 −0.000492441 −3.9561E−05 4.4766E−08 C26 X²Y⁴ 0.003450416−8.7915E−03 −0.025788093 2.6119E−05 5.4970E−09 C28 Y⁶ −0.0670923825.5329E−03 0.459287803 6.4168E−05 −9.7367E−10 C29 X⁷ −4.28869E−066.5180E−06 0.000509734 4.5678E−06 −2.2207E−09 C31 X⁵Y² −0.000659626−2.2057E−04 0.00031577 6.9710E−06 −2.6343E−10 C33 X³Y⁴ −0.0114488583.2124E−03 −0.000933577 7.0756E−06 −8.9063E−10 C35 XY⁶ −0.0665800546.3687E−03 0.046089419 −6.4576E−05 −6.8233E−11 C37 X⁸ −4.81707E−061.4610E−06 −0.000200734 −2.6466E−07 −2.8978E−10 C39 X⁶Y²  −7.6712E−05−5.9685E−05 −0.000125075 −4.2372E−06 −6.8633E−11 C41 X⁴Y⁴ 0.003204566−8.1972E−04 −0.000409066 4.6693E−06 −2.2445E−11 C43 X²Y⁶ −0.033227934−2.2869E−02 0.040759007 2.2739E−06 8.3163E−12 C45 Y⁸ 0.064497411−6.2588E−01 −0.432182695 9.1847E−07 7.3071E−13 C46 X⁹   2.9152E−08−2.3726E−08 −0.000232996 2.7004E−07 −2.4595E−12 C48 X⁷Y² −1.44485E−05−4.5344E−06 −5.20091E−06 1.1587E−06 6.3132E−12 C50 X⁵Y⁴ −0.000616877−4.2762E−05 0.00093 7.6834E−07 1.8258E−12 C52 X³Y⁶ 0.0107027981.0703E−02 −0.000219987 −1.7926E−06 5.6079E−13 C54 XY⁸ 0.048561261−1.6442E−01 −0.00049315 7.4764E−06 3.3298E−15 C56 X¹⁰   1.7083E−06−2.5101E−07 8.78141E−05 −7.1733E−08 2.6285E−15 C58 X⁸Y²   1.73327E−056.4384E−06 −9.79968E−06 −9.5138E−08 1.0107E−13 C60 X⁶Y⁴   8.56939E−053.9058E−06 −8.42942E−05 −2.2269E−07 −3.9928E−14 C62 X⁴Y⁶ −0.001672071.3904E−03 −0.000578202 2.2427E−07 −1.2971E−14 C64 X²Y⁸ 0.028208751.3481E−02 −0.013192328 −5.8871E−07 −3.7322E−15 C66 Y¹⁰ 0.0074772944.6528E−01 0.136172617 −7.2216E−07 −1.8566E−16

Table 2 indicates arrangement positions of an MEMS (resonant swing withhorizontal ±5.3° and vertical ±2.9°) as the scanning mirror 1, afreeform surface lens, and a freeform surface mirror from a laser sourceof each of optical elements that are a zeroth surface. Table 3 indicatesfreeform surface coefficients of a freeform surface shape defined byFormula 1 below.

$\begin{matrix}{Z = {\frac{c \cdot \left( {x^{2} + y^{2}} \right)}{1 + \sqrt{1 - {\left( {1 + K} \right){c^{2} \cdot \left( {x^{2} + y^{2}} \right)}}}} + {\sum{\sum\left( {{{Cj}\left( {m,n} \right)} \times x^{m} \times y^{n}} \right)}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

FIG. 27 is a view illustrating coordinates at which rays with scanningangles adjusted by a scanning mirror 1 having a swinging angle of ±5.3°in a main scanning direction and a swinging angle of ±2.9° in a verticalscanning direction reach the image plane 20 at 10° intervals of a phase.FIG. 27 indicates results obtained by evaluating a scanning area indetail by division of 19×19. A projection distance from the freeformsurface mirror 3 illustrated in FIG. 24 is 100 mm, and the scanning areaof 600×450 mm on the image plane 20 by the freeform surface is scanned.A state where improvement of linearity and an increase in angle arerealized at the same time can be understood.

Next, results of the improvement of linearity and the increase in anglefrom an incident angle and an incident coordinate on the image planewill be described with reference to FIG. 28 to FIG. 32 while beingcompared with the general resonance action that has already beenillustrated in FIG. 11 and FIG. 12 described above.

Note that FIG. 11 and FIG. 12 described above are respectively viewsillustrating the incident angle on the image plane and the incidentcoordinate on the image plane in a state where only a space forequivalent of the freeform surface lens 2 and the freeform surfacemirror 3 is provided at first. The incident angle sinusoidally changesin a range of ±10.6° that is a value twice 5.3°. Similarly, the incidentcoordinate also sinusoidally changes in a range of ±26.6 mm.

On the other hand, in FIG. 28 and FIG. 29, by largely changing theincident angle by means of actions of the freeform surface lens 2 andthe freeform surface mirror 3, an incident coordinate with a triangularwave shape in a range of ±300 mm on the image plane 20 is realized.Namely, a scanning area on a scan image surface is ±26.6 mm in aconventional system, while it is ±300 mm in the present embodiment,thereby realizing an increase in angle of more than ten times.

At this time, a horizontal size corresponding to a long side of thetwo-dimensional scanning area is X=600 mm, and a projection distance isL=100 mm. Therefore, a very small value L/X=0.17 is realized.

Note that the projection distance is defined by a length of aperpendicular line from a reference position to the image plane. Thereference position defines an arrangement position of freeform surfacemirror on lens data. However, in applications to give priority tominiaturization of the optical scanning video projecting apparatus 10,it is also effective to enlarge the value of L/X in a range notexceeding “1”.

Further, for the purpose of comparison, the conventional technology (seeJapanese Patent Application Publication No. 2010-139687 and JapanesePatent Application Publication No. 2005-234157 described above)describes an angle of view of ±18.9° symmetrical in a horizontaldirection. When the value of L/X is calculated on the basis of thisdescription, a large value is obtained by L/X=1/2/tan 18.9=1.46. It canbe understood that an increase in angle is insufficient in theconventional technology.

Next, characteristics of the freeform surface lens 2 and the freeformsurface mirror 3 will be described with reference to FIG. 30 and FIG.31.

FIG. 30 illustrates an area of a ray in which coordinates of a main rayexist as a control result of the ray by the freeform surface lens 2 andthe freeform surface mirror 3. Since a main scanning direction of thescanning mirror 1 is larger than a vertical scanning direction thereof,an area of the main ray on a fourth surface, which is an incidentsurface of the first freeform surface lens 2 a, becomes a horizontallylong area.

A state where the area of the main ray changes into a vertically longarea whenever a laser beam in turn passes through an emission surface ofthe first freeform surface lens 2 a and the second freeform surface lens2 b can be understood from this drawing.

Note that in an eighth surface that is the freeform surface mirror 3,the area becomes the vertically long area. However, the main scanningdirection (a horizontal direction in FIG. 30) is not narrowed extremelyin the eighth surface, but this results from a situation that a verticalsize on the eighth surface is made larger as a freedom degree.

This reason will be explained with reference to FIG. 31.

FIG. 31 is a ray diagram on a cross section of the main scanningdirection, and is a view illustrating the ray diagram of the wholeoptical system and an enlarged view of the freeform surface lens 2together. Swing of the scanning mirror 1 causes a ray L1 that passesthrough a positive side of an X axis in FIG. 31 to be reflected by thefreeform surface mirror 3 to reach a coordinate P1 on the image plane20. On the other hand, a ray L2 that passes through a negative side ofthe X axis is reflected by the freeform surface mirror 3 to reach acoordinate P2 on the image plane 20. Here, it is necessary that anoptical path of the ray L2 passing through the second freeform surfacelens 2 b and an optical path of the ray L1 reflected by the freeformsurface mirror 3 do not interfere in the second freeform surface lens 2b. In order to do this, it is necessary that a width formed by the rayL1 and the ray L2 on the freeform surface mirror 3 is to be madesmaller. This is a reason why a size of a ray passing range in ahorizontal direction on the freeform surface mirror 3 is made smaller.

Further, in the present embodiment, as illustrated in FIG. 31, anoptical path length of the ray L1 from reflection by the freeformsurface mirror 3 to the image plane 20 is larger than an optical pathlength of the ray L2. For this reason, image magnification is differentdepending upon a position of optical scanning, and linearity of ascanning image is thus deteriorated. In order to improve this, it isnecessary that the optical path length of the ray L1 is made shorterthan the optical path length of the ray L2 by the freeform surface lens2 and the freeform surface mirror 3.

Thus, in order to make the air-conversion optical path length of the rayL1 passing through the freeform surface lens 2 smaller than that of theray L2, lens thickness at a side that the ray L1 passes through was madethinner to form so-called spurious prism. A change amount of the opticalpath length that can be realized by causing the freeform surface lens 2to form the spurious prism is smaller compared with a difference of theoptical path length after the laser beam is reflected by the freeformsurface mirror 3. However, it would be effective to restrict the opticalpath length before the freeform surface mirror 3 on the design.

On the other hand, in a case where a lens shape of the freeform surfacelens 2 described above is formed as prism, an optical path thereafter isdifferent by a wavelength of light due to dispersion of lens material(that is, a refraction factor is different depending upon the wavelengthof light). Thus, a reach distance on the image plane is different forevery wavelength of light, chromatic aberration of magnification occurs.In order to reduce this chromatic aberration of magnification, in thefreeform surface lens 2 and the freeform surface mirror 3 describedabove, the optical path length of the ray L1 is made shorter than theoptical path length of the ray L2, and the air-conversion optical pathlength of the ray L1 passing through the freeform surface lens 2 is madeshorter than that of the ray L2. It was found by simulation that in acase where a ratio of the lens thickness at the side that the ray L1passes through and lens thickness at a side that the ray L2 passesthrough is set to three times or less, it is possible to reducechromatic aberration of magnification to a level of causing no problemin practical use. Moreover, in a case where it is set to within twice,it is possible to obtain further good imaging performance.

Image magnification is different depending upon the position of opticalscanning generated for a reason why the optical path length of the rayL1 from reflection by the freeform surface mirror 3 to the image plane20 is larger than the optical path length of the ray L2. Deteriorationof linearity of the scanning image can be reduced sufficiently byoptimization of a mirror shape of the freeform surface mirror 3 that hasa large freedom degree of design and optimization of a shape of thefreeform surface lens described above (power distribution).

On the other hand, characteristics in the vertical scanning directionwill be described with reference with FIG. 32. FIG. 32 is a view of asag amount by each of optical elements in a vertical scanning direction.In FIG. 32, each of the first freeform surface lens 2 a and the secondfreeform surface lens 2 b has negative refractive power in a concavelens shape. Further, a central portion of the freeform surface mirror 3has positive refractive power because of a concave surface, and aperipheral portion thereof has negative refractive power because of aconvex surface. This is because the vertical scanning direction is setto plane symmetrical arrangement in the lens data according to the firstembodiment. by changing a condition of plane symmetry, that is, anarrangement relationship, the portion of the positive refractive powerand the portion of the negative refractive power are changed. Thus,expression that a portion of positive refractive power and a portion ofnegative refractive power exist in the freeform surface mirror 3 iscorrect.

As described above, it can be understood that by arranging the freeformsurface lens 2 and the freeform surface mirror 3 in a predeterminedcondition, the swinging angle of the scanning mirror 1 can apparently beincreased to ten times or more, and improvement of linearity is realizedat the same time. In other words, it is possible to realize an opticalscanning apparatus with a super wide angle even though the swingingangle of the scanning mirror 1 is small. Mechanical reliability of theMEMS as the scanning mirror 1 is never impaired.

<Second Embodiment>

Next, a configuration of an optical system in an optical scanningapparatus according to a second embodiment will be described withrespect to FIG. 33 to FIG. 36, Table 4 and Table 5.

FIG. 33 is a basic optical configuration diagram according to the secondembodiment. FIG. 34 is an enlarged view of an optical scanning videoprojecting apparatus according to the second embodiment. FIG. 35 is anenlarged view of a freeform surface lens according to the secondembodiment. FIG. 36 is a distortion performance diagram according to thesecond embodiment. Further, Table 4 below denotes one example of lensdata according to the second embodiment. Table 5 denotes one example ofcoefficients of the freeform surface.

TABLE 4 DISTANCE NAME OF CONTENT OF SURFACE RADIUS OF BETWEEN GRASSECCENTRICITY NAME NUMBER SHAPE CURVATURE SURFACES MATERIAL AND FALLINGLASER LIGHT (0) SPHERE ∞ 5 SOURCE INCIDENT (1) SPHERE ∞ 0 PUPIL MEMS (2)SPHERE ∞ 0 REFLECTIVE DECENTER & SURFACE RETURN DUMMY (3) SPHERE ∞ −10NORMAL SURFACE ECCENTRICITY FREEFORM (4) XY −140.2019 −5 PMMA 25′DECENTER & SURFACE POLYNOMIAL RETURN LENS SURFACE (5) XY −87.9970 −50DECENTER & POLYNOMIAL RETURN SURFACE FREEFORM (6) XY −2074.526 0REFLECTIVE DECENTER & SURFACE POLYNOMIAL SURFACE RETURN MIRROR SURFACEDUMMY (7) SPHERE ∞ 100 NORMAL SURFACE ECCENTRICITY IMAGE PLANE (8)SPHERE ∞ 0 NORMAL ECCENTRICITY AMOUNT OF AMOUNT OF ECCENTRICITY (mm)FALLING (°) X Y AROUND AROUND SURFACE ECCENTRICITY ECCENTRICITY X AXIS YAXIS NAME NUMBER xde yde ade bde LASER LIGHT (0) SOURCE INCIDENT (1)PUPIL MEMS (2) 0 0 0 −39.818 DUMMY (3) 0 0 0 −90.000 SURFACE FREEFORM(4) 1.556 0 0 10.869 SURFACE (5) 1.808 0 0 −1.11 LENS FREEFORM (6)38.062 0 0 62.596 SURFACE MIRROR DUMMY (7) 0 0 0 127.800 SURFACE IMAGEPLANE (8) 270 0 0 0

TABLE 5 FREEFORM FREEFORM SURFACE SURFACE LENS MIRROR FOURTH FIFTH SIXTHCODE SURFACE SURFACE SURFACE c 1/R −0.007132572 −0.011364024−0.000482038 K K 0 0 0 C2 X 0.191070273 −0.35249979 −0.204793784 C4 X²−0.103663775 −0.007850465 −0.005957753 C6 Y² 0.567561957 −0.037196860.002400809 C7 X³ −0.007521603 −0.003417279 6.10749E−05 C9 XY²0.091876877 0.000517977 0.000192292 C11 X⁴ 0.004959388 2.6292E−04  7.5623E−06 C13 X²Y² −0.002077849 3.9894E−03 −1.6143E−06 C15 Y⁴−0.407964888 2.9205E−03 −7.7905E−07 C16 X⁵ −0.002088801 1.4189E−04  3.3066E−07 C18 X³Y² 0.003570485 −2.7959E−04 −4.7153E−07 C20 XY⁴−0.142157669 −7.1242E−04   1.7743E−07 C22 X⁶ 0.000829819 1.5620E−06  3.2352E−08 C24 X⁴Y² 0.000617828 −4.3309E−05   6.5997E−10 C26 X²Y⁴−0.000686478 5.7570E−05   3.3298E−09 C28 Y⁶ 0.626930796 3.7339E−06−2.9924E−09 C29 X⁷ 0.001104665 3.0946E−06 −7.2033E−10 C31 X⁵Y²0.001174248 2.8098E−06   3.6755E−10 C33 X³Y⁴ −0.003606619 4.8514E−06−8.1503E−10 C35 XY⁶ 0.123222494 −8.9434E−05 −2.6672E−10 C37 X⁸−0.000403152 −5.6393E−07 −1.1905E−10 C39 X⁶Y² 0.000245671 −5.2579E−06−7.9248E−11 C41 X⁴Y⁴ −0.007652178 3.6503E−06 −1.2810E−11 C43 X²Y⁶0.032961649 8.1001E−07   1.3911E−11 C45 Y⁸ −0.590578953 9.9163E−06  3.2946E−12 C46 X⁹ −0.0002447 2.4449E−07 −9.9787E−13 C48 X⁷Y²−0.000655028 1.1531E−06   4.6133E−12 C50 X⁵Y⁴ 0.001749715 5.5272E−07  1.3281E−12 C52 X³Y⁶ −0.006489721 −2.3944E−06   1.1915E−12 C54 XY⁸−0.041212334 6.2778E−06   7.9863E−14 C56 X¹⁰ 0.00011303 −5.5414E−08−2.6446E−13 C58 X⁸Y² 0.00026706 −1.7895E−08   2.4070E−13 C60 X⁶Y⁴−0.000981428 −2.3583E−07 −8.1436E−14 C62 X⁴Y⁶ 0.007212128 3.7389E−07−2.2139E−14 C64 X²Y⁸ −0.026269329 −3.1933E−07 −1.1348E−14 C66 Y¹⁰0.271096853 −7.0287E−07 −1.1555E−15

Note that in this second embodiment, the freeform surface lens 2 isconfigured by one piece, and the other points are similar to thoseaccording to the first embodiment described above.

<Third Embodiment>

Moreover, a configuration of an optical scanning apparatus according toa third embodiment will be described with reference to FIG. 37 to FIG.40.

FIG. 37 is a basic optical configuration diagram according to the thirdembodiment. FIG. 38 is an enlarged view of an optical scanning videoprojecting apparatus according to the third embodiment. FIG. 39 is anenlarged view of a freeform surface lens according to the thirdembodiment. FIG. 40 is a distortion performance diagram according to thethird embodiment. Further, Table 6 below denotes one example of lensdata according to the third embodiment. Table 7 denotes one example ofcoefficients of the freeform surface.

TABLE 6 DISTANCE NAME OF CONTENT OF SURFACE RADIUS OF BETWEEN GRASSECCENTRICITY NAME NUMBER SHAPE CURVATURE SURFACES MATERIAL AND FALLINGLASER LIGHT (0) SPHERE ∞ 5 SOURCE INCIDENT (1) SPHERE ∞ 0 PUPIL MEMS (2)SPHERE ∞ 0 REFLECTIVE DECENTER & SURFACE RETURN DUMMY (3) SPHERE ∞ −8.5NORMAL SURFACE ECCENTRICITY FREEFORM (4) XY ∞ −2.7 PMMA 25′ DECENTER &SURFACE POLYNOMIAL RETURN LENS SURFACE (5) XY ∞ −0.981 DECENTER &POLYNOMIAL RETURN SURFACE FREEFORM (6) XY ∞ −3.5 PMMA 25′ DECENTER &SURFACE POLYNOMIAL RETURN LENS SURFACE (7) XY ∞ −59.819 DECENTER &POLYNOMIAL RETURN SURFACE FREEFORM (8) XY ∞ 0 REFLECTIVE DECENTER &SURFACE POLYNOMIAL SURFACE RETURN MIRROR SURFACE DUMMY (9) SPHERE ∞ 100NORMAL SURFACE ECCENTRICITY IMAGE PLANE (10) SPHERE ∞ 0 NORMALECCENTRICITY AMOUNT OF AMOUNT OF ECCENTRICITY (mm) FALLING (°) X YAROUND AROUND SURFACE ECCENTRICITY ECCENTRICITY X AXIS Y AXIS NAMENUMBER xde yde ade bde LASER LIGHT (0) SOURCE INCIDENT (1) PUPIL MEMS(2) 0 0 0 −40.865 DUMMY (3) 0 0 0 −90.000 SURFACE FREEFORM (4) −0.094 00 22.012 SURFACE (5) 0.337 0 0 5.086 LENS FREEFORM (6) 1.990 0 0 21.457SURFACE (7) 2.322 0 0 −4.297 LENS FREEFORM (8) 62.309 0 0 80.113 SURFACEMIRROR DUMMY (9) 0 0 0 129.307 SURFACE IMAGE PLANE (10) 270 0 0 0

TABLE 7 FREEFORM FREEFORM FREEFORM SURFACE SURFACE LENS SURFACE LENSMIRROR FOURTH FIFTH SIXTH SEVENTH EIGHTH CODE SURFACE SURFACE SURFACESURFACE SURFACE c 1/R 0 0 0 0 0 K K 0 0 0 0 0 C2 X 0.3467445270.26782264 −0.180273253 −0.309131769 −0.631304397 C4 X² 0.04252678−0.013311811 −0.055711788 0.003492276 −0.009243924 C6 Y² −0.155063178−0.054453872 0.832549045 0.021625569 0.002365015 C7 X³ −0.0216347780.004038403 0.005476125 −0.005649828 0.000687608 C9 XY² −0.0139032680.020147273 0.095469608 −0.006145659 0.000233248 C11 X⁴ −0.0008516846.1694E−04 0.005660408 1.8017E−04 1.6596E−05 C13 X²Y² 0.0131171778.0799E−03 0.019905661 2.9934E−03 −1.1722E−05 C15 Y⁴ −0.019803254−2.9061E−01 −0.443797536 2.2993E−03 −9.8768E−07 C16 X⁵ 0.0001057731.1159E−04 −0.000171959 1.3871E−04 −9.5748E−07 C18 X³Y² −0.0028894217.2556E−03 −0.00221254 −3.7959E−04 −6.2226E−07 C20 XY⁴ 0.0384436158.7639E−02 −0.084230933 −6.8728E−04 8.0919E−08 C22 X⁶   4.31381E−052.3962E−05 0.000295724 4.9598E−06 2.3519E−08 C24 X⁴Y² 0.003062574−4.5787E−04 −0.000316974 −3.9453E−05 4.6828E−08 C26 X²Y⁴ 0.006110861−1.2666E−02 −0.025609184 2.1866E−05 5.6518E−09 C28 Y⁶ −0.062935333−1.1715E−01 0.45537754 7.4176E−05 −9.1435E−10 C29 X⁷  −4.4624E−066.7419E−06 0.00050416 4.5761E−06 −2.6301E−09 C31 X⁵Y² −0.000620824−2.3565E−04 0.00026525 7.1689E−06 −2.3094E−10 C33 X³Y⁴ −0.0109733232.2225E−03 −0.000248937 6.8180E−06 −8.5694E−10 C35 XY⁶ −0.0655814652.4661E−02 0.045870765 −6.3356E−05 −6.2195E−11 C37 X⁸ −4.84041E−061.5208E−06 −0.000200859 −2.6322E−07 −3.5249E−10 C39 X⁶Y² −7.42022E−05−6.2873E−05 −1.54748E−05 −4.2365E−06 −6.3592E−11 C41 X⁴Y⁴ 0.002800899−8.1854E−04 −0.000783594 4.6472E−06 −2.1806E−11 C43 X²Y⁶ −0.031790714−1.9997E−02 0.039158598 2.2779E−06 8.3537E−12 C45 Y⁸ 0.059212604−7.1397E−01 −0.411847122 7.4042E−07 7.3022E−13 C46 X⁹   6.27795E−08−1.5713E−08 −0.000233248 2.6990E−07 −2.9044E−12 C48 X⁷Y² −1.82739E−05−4.5629E−06 1.16318E−06 1.1549E−06 8.3784E−12 C50 X⁵Y⁴ −0.000499521−1.6187E−05 0.000915373 7.9373E−07 1.9435E−12 C52 X³Y⁶ 0.0116489321.1649E−02 −5.05992E−05 −1.8391E−06 5.7069E−13 C54 XY⁸ 0.057087544−1.5520E−01 −0.005093218 7.7288E−06 1.8796E−15 C56 X¹⁰    1.744E−06−2.5337E−07 8.77099E−05 −7.1972E−08 −3.3208E−14 C58 X⁸Y²   1.58227E−056.8173E−06 −1.94823E−05 −9.7713E−08 1.1231E−13 C60 X⁶Y⁴ 0.0001042131.4834E−05 −7.59028E−05 −2.1420E−07 −5.2882E−14 C62 X⁴Y⁶ −0.0020431731.2694E−03 −0.000559016 2.0402E−07 −1.6189E−14 C64 X²Y⁸ 0.024744197−1.3458E−03 −0.012352595 −5.7551E−07 −3.8572E−15 C66 Y¹⁰ 0.0093460227.0781E−01 0.127910068 −7.8724E−07 −2.0337E−16

In this third embodiment, a swinging angle (resonant swing withhorizontal ±5.3° and vertical ±2.9°) of an MEMS as a scanning mirror 1is essentially for a wide screen of 16:9, and a size of an image planeis thus set as a two-dimensional area of 800×450 mm by 16:9. Only thepoint is different from that according to the first embodiment describedabove. As is apparent from FIG. 40, linearity that is distortionperformance is greatly improved compared with FIG. 27 indicatinglinearity that is distortion performance according to the firstembodiment. In the scanning mirror 1 that has been developed to scan animage plane of 16:9, it is essentially good to scan the image plane of16:9 as combination. However, to the contrary, it can be said that thescanning mirror that has been developed as 16:9 can also be applied toan image plane of 4:3 in the configuration in which the freeform surfacelens 2 and the freeform surface mirror 3 are used according to thepresent invention.

<Other Modification Example>

FIG. 41 and FIG. 42 are explanatory drawings illustrating a first usageform of the other modification example of the optical scanningapparatus. FIGS. 41 and 42 are respectively a top view of the opticalscanning apparatus including a scan image surface and a side viewthereof.

This usage form according to the modification example has aconfiguration in which an optical scanning video projecting apparatus 10including a housing 40 is arranged at an effective upper portion of ascan image surface 20. FIGS. 41 and 42 illustrate a state where laserbeams reach divided points of 5×5 on the scan image surface 20. However,only an X axis direction is narrowed from an area (which is displayed bya dashed-dotted line 31 in FIG. 41), to which an effective scanning areain the vicinity of the optical scanning video projecting apparatus 10 iseffectively assigned, so that the scanning laser beams do not overlapthe optical scanning video projecting apparatus 10. As a result, afreedom degree of installation of the optical scanning video projectingapparatus 10 becomes larger. In addition, even though a size of theoptical scanning video projecting apparatus 10 including the housing 40becomes large, a set does not cut off a scanning image in an actualusage state, whereby it is possible to improve usability thereof.

Further, even though the optical scanning video projecting apparatus 10is arranged in a vertical direction of a scan screen (in a longitudinaldirection of the scan screen in FIG. 41), in the optical scanningapparatus described above and an image display apparatus using this, theset does not cut off the scanning image in the actual usage state due tothe above reason.

FIG. 43 is an explanatory drawing illustrating a second usage form ofthe other modification example. A difference from the first usage formillustrated in FIG. 41 is that a plurality of optical scanningapparatuses 10-1 and 10-2 are arranged at different positions of thescan screen (in FIG. 43, two are arranged for convenience ofexplanation). In the present usage form, the optical scanningapparatuses 10-1, 10-2 can be arranged without cutting off a scan screendisplay area. Therefore, by using a plurality of optical scanningapparatuses to display the same scanning image and overlap the screens,it is possible to become high luminance.

Further, by intendedly shifting scanning image positions of theplurality of optical scanning apparatuses each having the sameresolution, it is possible to view the scanning image so as to increaseresolution thereof artificially. By interlacing and creating a scanningimage by image information for different fields to overlap the screens,it is possible to improve the resolution thereof.

FIG. 44 is an explanatory drawing illustrating a third usage form of theother modification example. In FIG. 44, optical scanning apparatuses10-2, 10-3 can be arranged without cutting off a scan screen displayarea. Therefore, by using the plurality of optical scanning apparatusesto display the same scanning image and overlap the screens, it ispossible to obtain the similar effects to those in the second usage formdescribed above.

In the rear system projection board apparatus (that is, rear projectionvideo display apparatus) illustrated in FIG. 1 to FIG. 3 according toone embodiment of the present invention or the so-called small frontsystem projection board apparatus (that is, front projection videodisplay apparatus) for table use, which can be mounted on a top surfaceof a table or the like, illustrated in FIG. 4 to FIG. 6 according toanother embodiment of the present invention, the usage form illustratedin FIG. 44 is the better, for example. At this time, it is desirablethat a plurality of optical scanning apparatuses or a single opticalscanning apparatus is arranged at a lower portion of the projectionboard apparatus in consideration of stability of the set. However, theoptical scanning apparatuses may be arranged in a horizontal directionof the screen as illustrated in FIG. 44 in accordance with an aspectratio of the screen.

Moreover, in a case where a laser beam of one optical scanning apparatusis set to one polarized wave (for example, P wave), a laser beam of theother optical scanning apparatus is set to the other polarized wave (forexample, S wave), and video for a right eve and video for a left eye arerespectively set to the scanning images, then it is possible to overlapthe screens by using polarization glasses to enjoy a stereoscopic image.

Similarly, by respectively sending video for a right eye and video for aleft eye to one optical scanning video projecting apparatus 10 and theother optical scanning apparatus as the scanning images and usingspecial glasses provided with a function to overlap the screens andswitch images respectively entering the right and left eyes in timedivision, it is possible to enjoy a stereoscopic image.

<Uniformity in Brightness of Scan Screen>

Next, a technique to make brightness of a scan screen uniform will bedescribed below. FIG. 45 is an explanatory drawing for explaining itsprinciple. Scanning of a laser beam emitted from the light source 4 (seeFIG. 20), which is a main part constituting an optical scanning videoprojecting apparatus 10 b, is deflected by swing of the scanning mirror1 (see FIG. 20), and then, the laser beam is respectively refracted andreflected by the freeform surface lens 2 (see FIG. 20) and the freeformsurface mirror 3 (see FIG. 20) to reach a scan image surface 20.

The laser beam emitted from the optical scanning video projectingapparatus 10 b has a spot size (corresponding to one pixel) 201 having aspecific size. As illustrated in FIG. 46, a laser beam 204 is scanned onthe scan image surface 20 along an arrow 202 in a horizontal directionduring first scanning and along an arrow 203 in a reverse directionthereto during second scanning. Thus, since there is no flyback periodunlike an interlace system, there is no loss in the scanning time. As aresult, resolution thereof is never impaired. As a laser source, asemiconductor laser is configured by a clad layer 402 put betweenelectrodes 401 and 404 and an active region 403 that exists in the cladlayer 402 as illustrated in FIG. 47, for example. A spot shape 405 ofthe emitted laser beam becomes an elliptical shape in which a directionorthogonal to the active region 403 that exists in the clad layer 402 (Yaxis in FIG. 47) is a longitudinal direction thereof.

For this reason, in a case where the semiconductor laser whose spotshape becomes an elliptical shape is used as the laser source, asillustrated in FIG. 48, by matching a short side of the ellipsoid spotshape with a direction of a far distance on the scan screen with respectto the optical scanning apparatus (that is, a longitudinal direction inFIG. 48), it is possible to reduce deterioration of the spot shape dueto oblique incidence.

Note that, in the conventional technology, as described above,resolution performance was unambiguously determined on the basis of asize of the scan screen determined by an oscillation angle of a scanningmirror when a spot size of the laser beam is determined.

On the other hand, in the optical scanning video projecting apparatus 10b provided with the configuration described above, a final surface of anoptical system is configured by a reflective surface. Thus, a laser beamscanned and deflected by a scanning mirror undergoes deflection twice anincident angle on the reflective surface of the mirror. For that reason,it is possible to deflect the laser beam largely with respect todisplacement magnitude of the scanning mirror, and it is possible torealize a peculiar feature that an angle with respect to a normal lineof a surface of a corresponding freeform surface mirror isdifferentiated depending upon a corresponding position of the scanscreen so that a reflection angle of the freeform surface mirror isdifferent from each other. For this reason, unlike the conventionaltechnology, resolution is not determined only by a spot size of thelaser beam and an oscillation angle of the scanning mirror.

Moreover, in the optical scanning video projecting apparatus 10 bdescribed above, the laser beam enters each position of the scan screenwith a different incident angle. Therefore, there is need to change eachof the spot size of the laser beam and luminance or density inaccordance with the scanning position independently or by combiningthem.

Next, first technical means for embodying the content described abovewill be described.

In the first technical means, as illustrated in FIG. 48, an opticalscanning video projecting apparatus 10 a is configured by combining aplurality of laser sources. However, for convenience of explanation, acase of two kinds will be described herein.

According to the configuration illustrated in FIG. 48, light from afirst light source 4 a and light from a second light source 4 b aresynthesized by a light synthesizer 5 a. After the synthesized light isscanned and deflected by means of swing of a scanning mirror 1, thelight is refracted by the freeform surface lens 2 (see FIG. 20) andreflected by the freeform surface mirror 3 (see FIG. 20) to reach thescan image surface 20. By using a polarized light synthesis prism as thelight synthesizer 5 a, for example, and respectively setting a laserbeam from the first light source 4 a and a laser beam from the secondlight source 4 b to a P-polarized wave and an S-polarized wave, it ispossible to synthesize the laser beams effectively.

Moreover, by Generating the P-polarized wave as laser beams of asynthesis optical system or multiple light emitting laser, whichsynthesizes the laser beams with different wavelengths of RGB oscillatedby laser sources in the first light source 4 a, and by similarlygenerating the S-polarized wave as laser beams of a synthesis opticalsystem or multiple light emitting laser, which synthesizes the laserbeams with different wavelengths of RGB oscillated by laser sources inthe second light source 4 b, it is possible to synthesize the laserbeams effectively and display color video.

Namely, by changing optical outputs of the laser beams emitted from thefirst and second laser sources 4 a, 4 b in accordance with a position ofthe scan screen, it is possible to improve uniformity of luminance ofthe whole screen. Note that in order to obtain a high optical outputwithout impairing its reliability, this can be realized by causingcurrent exceeding a rated value to flow in a pulse manner for a specificshort period. It goes without saying that at this time, a spot diameterof the synthesized laser beam may also be changed while beingsynchronized with an output of the laser beam of each of the lightsources.

FIG. 49 is a principle view for explaining the first technical means tomake brightness on the scan screen uniform. An optical scanningapparatus (not illustrated in the drawings) is used to carry out firsthorizontal scanning along an arrow 202 while making resolution power ina vertical direction of the screen finer, and carry out second scanningalong an arrow 203-1 and an arrow 203-2 of a reverse direction. At thistime, the laser beam is not emitted (or oscillated) in a region of thearrow 203-1 (which is displayed by a broken line in FIG. 49). As aresult, it becomes possible to relatively increase brightness of thescreen in a left side of FIG. 49. Similarly, it goes without saying thata region in which the laser beam is to be emitted (or oscillated) canalso be controlled freely by changing brightness of a part of the screen(for example, a right side or upper and lower portions) or tilting achange amount of brightness.

Moreover, second technical means for embodying the content describedabove will be described. FIG. 50 is a principle view for explaining thesecond technical means for making brightness on the scan screen uniform.A difference from the first technical means illustrated in FIG. 49described above is that an optical scanning apparatus (not illustratedin the drawings) is used to scan a laser beam in a vertical direction ofthe screen.

In a case where the semiconductor laser whose spot shape becomes anelliptical shape is used as the laser source, by matching a short sideof the ellipsoid spot shape of the laser beam 204 with a direction of afar distance on the scan screen with respect to an optical scanningapparatus (not illustrated in the drawings) (that is, a longitudinaldirection in FIG. 50), it is possible to reduce deterioration of thespot shape due to oblique incidence. Further, in order to makebrightness in the scan screen uniform, for example, by changing ascanning interval in the longitudinal direction of the screen between ascanning area in an area A and a scanning area in an area B asillustrated in FIG. 51, it becomes possible to relatively increasebrightness of the screen at a left side of the scan screen. Similarly,it goes without saying that the laser beam is to be emitted (oroscillated) can also be controlled in the scanning area in the verticaldirection of the screen freely by changing brightness of a part of thescreen (for example, a right side or upper and lower portions) ortilting a change amount of brightness.

Next, a technique to reduce speckles will be described below. Aseffective technical means for reducing speckles, three technical meansdescribed below are effective.

(1) A coherent laser beam is converted into irregular light temporallyand/or spatially.

(2) Light with a plurality of wavelengths is mixed without using lightwith a single wavelength.

(3) intensity of light is changed temporally and/or spatially togenerate irregular light.

As one of concrete technical means that realizes (1) and (3) describedabove, by controlling surface roughness of a surface of a freeformsurface mirror used in an oblique project optical system of the opticalscanning apparatus, speckles, which are random interference patterns ofthe laser beam, are suppressed from being generated.

Its realization is achieved by molding plastic and providing reflectioncoating onto a surface thereof. For this reason, surface roughness of amold surface can be transferred to surface roughness of a reflectivesurface of the mirror as it is. Therefore, by controlling the surfaceroughness of the mold surface, it is possible to reduce speckles.

Note that, as illustrated in FIG. 52, an electrostatic type pressuresensor (electrostatic capacitive touch panel) can be incorporated on asurface of the screen 130. More specifically, as illustrated in FIG. 52,this electrostatic type pressure sensor is configured by installing asensor panel 131 on the surface of the screen 130 and mounting a hardcover (panel) 133 such as glass or acryl on a sensor surface viatransparent ITO 132. For example, in an electrostatic capacitive type,by reading a change in electrostatic capacity of a sensor circuit, acoordinate position is detected and read. Further, in a surface type, ina state where voltage is applied to electrodes of four corners to forman even electric field on a panel surface, by reading a change in theelectric field when a finger is touched, it becomes possible to detect acoordinate position.

By incorporating such an electrostatic capacitive touch panel thereon,for example, in a case where the projection board apparatus according tothe present invention is used to display an image of a personal computeron the screen 130, it is possible to carry out an operation of thepersonal computer by touching the screen 130 by means of the finger of auser.

Although the various embodiments have been explained in detail, thepresent invention is not limited to only the embodiments describedabove. Various modification examples may be included therein. Forexample, in the above embodiments, the whole apparatus has beendescribed in detail for clearly explaining the present invention.However, the apparatus is not necessarily limited to one provided withthe whole configuration that has been explained. Further, a part of theconfiguration of a certain embodiment can be replaced by theconfiguration of the other embodiment, and the configuration of theother embodiment can be added to the configuration of a certainembodiment. Further, the other configuration can be added to, removedfrom, or replaced by a part of the configuration of each of theembodiments.

REFERENCE SINGS LIST

1 . . . optical scanning unit, . . . scanning mirror, 2 . . . freeformsurface lens, 3 . . . freeform surface mirror, 4 . . . light source, 5 a. . . light synthesizer, 10 . . . optical scanning video projectingapparatus, 10 a, 10 b, 10-1, 10-2, 10-3 . . . optical scanningapparatus, 20 . . . image plane, 40 . . . housing, 61 . . . optical pathchanger, 63 . . . inclined surface, 113 . . . screen holder (stand), 130. . . projection screen (semitransparent screen), 401, 404 . . .electrode, 402 . . . clad layer, and 403 . . . active region.

The invention claimed is:
 1. A projection video display apparatuscomprising: a video projection screen that is arranged in an indoorspace in a state where, both a rear surface and a front surface of theprojection screen are exposed to the indoor space wherein the videoprojection screen is configured to: guide a video light toward the frontsurface of the video projection screen, and cause part of the light inthe indoor space to be transmitted therethrough; and a video projectorarranged at a predetermined position on a side of the rear surface orthe front surface of the video projection screen, wherein the videoprojector is configured to: enlarge and project a video from the rearsurface or the front surface of the video projection screen by scanningthe video light on the video projection screen, wherein the video lightis obtained from light with a specific wavelength alone or bysynthesizing the light with the specific wavelength, and wherein thevideo projection screen includes a reflection layer, with a reflectionfactor that is set with respect to a specific polarized wave included inthe video light.
 2. The projection video display apparatus according toclaim 1, wherein the reflection layer is formed on a whole displaysurface of the rear surface of the video projection screen, and thereflection layer is configured to guide the video light in apredetermined direction.
 3. The projection video display apparatusaccording to claim 2, wherein the reflection layer is configured byforming reflection coating on a part of a circular Fresnel lens or alinear Fresnel lens that is formed on an entirety of the rear surface ofthe video projection screen.
 4. The projection video display apparatusaccording to claim 1, wherein the reflection layer includes a circularFresnel lens formed on an entirety of the rear surface of the videoprojection screen, wherein a center of the circular Fresnel lens ispositioned outside an external form of the video projection screen. 5.The projection video display apparatus according to claim 1, wherein thevideo light is composed of coherent light and emitted as an S-polarizedlight wave.
 6. The projection video display apparatus according to claim5, wherein the projector includes: a light source configured to supply acoherent light beam; an optical scanning unit configured to scan thelight beam emitted from the light source by reciprocatingly swingingmovement of a reflective surface; and an optical scanning unitconfigured to carry out optical scanning for the light beam emitted fromthe light source of a two-dimensional scanning area in an image plane intwo directions by the reciprocatingly swinging movement of thereflective surface, the two directions including a long side directionthat is a main scanning direction and a short side direction that is avertical scanning direction.
 7. The projection video display apparatusaccording to claim 6, wherein the projector further includes: an opticalsystem between the optical scanning unit and the image plane, theoptical system being configured to enlarge a scanning angle of thescanned light beam, and wherein the optical system at least includes onecurved surface lens at a side of the optical scanning unit and onecurved surface mirror at a side of the image plane in a plane differentfrom a first plane, the first plane being defined by an incident ray anda reflected ray in the curved surface mirror when the optical scanningunit remains stationary at a center of the scanning area.
 8. Theprojection video display apparatus according to claim 1, furthercomprising: a sensor configured to detect a position coordinate that afinger of a user touches the video projection screen.
 9. The projectionvideo display apparatus according to claim 8, wherein the sensor iscomposed of an electrostatic type pressure sensor.